None of the 137 passengers was injured in the incident on the afternoon of January 30 this year, the report from the Air Accidents Investigation Branch (AAIB) said.

The incident occured in January

The report said that in pre-flight preparations, the flight crew noted that only low levels of turbulence were forecast, ''although there had been a report of severe turbulence over the Alps at FL (flight level) 220 (22,000ft)''.

The report went on: ''During the descent, the flight crew asked ATC (air traffic control) if there were any turbulence reports along their intended track and were told that light to moderate turbulence had been reported.

None of the 137 passengers was injured

''The commander (captain) warned the cabin crew of the possibility of turbulence and instructed them to secure the cabin. A few minutes later, passing FL220, the aircraft had two brief but severe clear-air turbulence encounters in quick succession.''